HCFCs, chemical species slated to replace
CFCs in the near future in most Western nations. When the normal
chlorofluorocarbons (see above) reach the stratosphere and are photo-decomposed,
their released chlorine radicals destroy the natural ozone that acts as our
umbrella to shield the Earth from ultraviolet radiation (see chlorine and
ozone). With one or more hydrogen-carbon bonds, HCFCs are still useful as
replacement for CFCs in most applications. However, this bonding structure makes
HCFCs much more chemicallyy unstable--as compared to CFCs--and therefore subject
to hydroxyl radical and ozone attack early in their gas phase career in the
atmosphere. In fact they react in the troposphere instead of the stratosphere.
Their atmospheric lifetime is shorter than CFCs and they, therefore, have a
smaller chance of reaching the stratosphere where their chlorine could be
released by destructive photolysis and enter the catalytic ozone destruction
cycle.